Heretofore, three broad classes of methods have been used to break down materials into smaller pieces: mechanical methods, chemical methods, and physio-chemical methods.
Mechanical methods made use of hammers, crushers, grinders, roll mills, ball mills, jet mills, and other impact or pressure devices to break raw materials into smaller pieces. For example, a rock crusher would be used to break boulder-sized rock into sand and gravel, or a grinding mill or chipper would be used to break raw lumber into wood chips. These methods were loud, resulted in high wear and tear on the mechanical equipment, and were energy intensive. They also had a limited size range, i.e. a rock crusher would not be effective at producing colloidal-sized particles; a wood chipper could not make chips much finer than sawdust; a jet mill would not be effective at breaking down boulder-sized rocks.
Chemical methods made use of chemical reactions to break raw materials into smaller pieces by reacting chemically with the raw materials, or by producing expansive or explosive chemical reactions to break apart the raw materials. The chemical methods that reacted chemically with the raw materials were limited by the surface area of the raw materials, and therefore often were combined with other mechanical or chemical methods to achieve the desired result, i.e. a wood chipper would be used to break raw lumber into sawdust prior to using chemical reactions (the "Kraft" method) to remove lignin from cellulose to produce paper pulp. Many chemical reactions resulted in un-wanted toxic or hazardous by-products, which often resulted in pollution or high disposal costs. Once the chemical reactions had taken place, the reactants were used up and could not be re-used or easily recycled. Expansive or explosive chemical reactions had a limited size range, i.e. dynamite could be used to quarry rock, but would not be effective at producing colloidal-size particles. Explosive reactions were often noisy and the shock waves from the explosives resulted in sometimes dangerous or annoying vibrations being felt at some distance from the explosion. Once the explosive reactions were complete, the explosives could not be re-used. In addition, explosive chemical reactions are inherently dangerous. All of these problems often resulted in special permitting requirements in order to protect the public from pollution from chemical methods or the dangers of explosives, all of which increased the costs associated with their use.
Several physio-chemical methods have been used to comminute raw materials. One physio-chemical method has been previously used to break down raw materials down into smaller pieces: freezing and thawing. For example, holes were drilled into native rock, filled with water, the filled holes were plugged, and then the water was frozen. The 9 percent volume increase when water freezes to ice resulted in pressure within the drilled holes and tensile stresses within the native rock. When several holes were strategically placed in a linear pattern, the combined tensile stresses within the native rock resulted in splitting along the line. However, freezing is a relatively slow method, so plugs were required to prevent drainage which would otherwise have relieved any pressures that built up during freezing. In addition, freezing the water called for waiting for a period of freezing weather, or in bringing the temperature of a large mass of rock or other materials to freezing temperatures. Whether applied to rock or other materials, these methods were wasteful of time and/or energy.
Another physio-chemical method of comminution is heat-treatment, as exemplified by U.S. Pat. No. 4,501,818, for hydrothermal comminution of zirconia or hafnia. Heat-treatment combined with hidriding is described by U.S. Pat. No. 4,760,966, for comminuting rare earth magnet alloys. These types of materials are difficult to comminute with mechanical methods because of the toughness of the raw materials. These methods rely on heating and cooling the raw materials or on volume changes caused by chemical reactions with the raw materials to induce stresses within the raw materials of sufficient magnitude to result in comminution. These methods are suited for a limited number of materials and are cost-effective for limited size ranges of raw materials and comminuted product.
Another physio-chemical method of comminuting non-swelling clay minerals consists of applying intercalation-forming products to the minerals, as described by U.S. Pat. No. 3,508,613. Negatively-charged clay minerals adsorb positive cations, which attract polar water molecules, resulting is swelling. This method is appropriate for clay minerals only.
Accordingly, the objects of the invention are to break down raw materials with physio-chemical methods that are quieter, recyclable, non-explosive, more energy efficient, safer, result in less mechanical wear, and which are effective over a wide range of sizes and types of raw materials.